Hydrophobic permeable composite, method for producing said composite and use of the same

ABSTRACT

The invention relates to a hydrophobic permeable composite, to a method for producing a hydrophobic permeable composite and to the use of said composite in various processes. Hydrophobic, permeable materials have been known for some time. Plastic materials especially, for example Gore-Tex®, but also materials consisting of other organic polymers are used whenever a material is required to be gas- and steam-permeable but not liquid-permeable. These materials have the disadvantage that they can only be used within a certain temperature range. The inventive composite is characterised by a higher temperature resistance since it consists mainly of inorganic materials. It is also relatively easy to produce since it can be obtained using the sol-gel technique. The inventive composite can be used as a membrane in the oxidation of aromatics, for example in the direct oxidation of benzene to phenol.

The invention relates to a permeable composite material havinghydrophobic properties, to a process for making this permeable compositematerial and to use of the same.

Hydrophobic permeable materials have been known for many years.Membranes of Teflon (Gore-Tex®) can be cited in particular in thisconnection, although membranes of other organic polymers are also known.These are suitable for a broad scope of application, based on theprinciple that substances pass through the porous material exclusivelyin the form of gas or vapor, but not of fluid. Such materials are made,for example, by stretching Teflon sheets, whereby ultra-fine cracks areformed which subsequently allow the passage of vapor or gas. Waterdroplets are held back by the hydrophobic material, since high surfacetension and the lack of wettability of the surfaces of the hydrophobicmaterials prevent them from penetrating into the pores.

Such hydrophobic materials are suitable not only for gas and vaporpermeation but also for membrane distillation. Furthermore, they areused as inert filter materials in many applications.

A disadvantage of these materials, however, is always the limitedtemperature range in which they can be used. In contrast, inorganicfilter materials are much more thermally stable, although they are oftenmore hydrophilic as well.

Very many substances can be made hydrophobic by subsequent hydrophobingof the most diverse inorganic substrates by means of reactive componentssuch as silanes or alkyl or fluoroalkyl compounds or by deposition ofprecursor products from the gas phase (CVD), but hydrophobing ispossible only in a subsequent process step. To some extent this step isquite complex, and so hydrophobing during the actual process ofproduction of inorganic filter materials would be advantageous.Furthermore, hydrophobing of large surfaces by the CVD technique isimpossible or possible only with considerable expense.

The object Of the present invention was therefore to provide a permeablecomposite material which exhibits hydrophobic properties and has verymuch smaller pores and very much greater thermal stability than theknown materials. Another object was to provide a simple process formaking such a composite material.

It has been surprisingly found that it is possible in simple manner, bymeans of the sol-gel method, to hydrophobe a permeable compositematerial based on at least one porous and permeable support, which isprovided on at least one side of the support and in the interior of thesupport with at least one inorganic component, which containssubstantially at least one compound of a metal, a semi-metal or a mixedmetal with at least one element of Group 3 to Group 7, and that such acomposite material exhibits high thermal stability.

The subject matter of the present invention is therefore a permeablecomposite material based on at least one porous and permeable support,which is provided on at least one side of the support and in theinterior of the support with an inorganic component, which containssubstantially a compound of a metal, a semi-metal and/or a mixed metalwith at least one element of Group 3 to Group 7, which material ischaracterized in that it exhibits hydrophobic properties.

Also subject matter of the present invention is a method for making apermeable composite material according to one of claims 1 to 9, in whichat least one suspension which contains at least one inorganic componentcomprising at least one compound of at least one metal, one semi-metalor one mixed metal with at least one of the elements of Group 3 to Group7 and a sol, is applied on at least one porous and permeable support,and this suspension is solidified on or in or on and in the supportmaterial by at least one heat treatment, which process is characterizedin that at least one of the inorganic components used exhibitshydrophobic properties and/or at least one hydrophobic material and/orone hydrophobing agent is added to the sol and/or to the suspension.

Further subject matter of the present invention is the use of acomposite material according to at least one of claims 1 to 9 as amembrane for membrane distillations.

The composite material according to the invention has the advantage thatit can also be used at higher temperatures than in the case of thematerials known heretofore. Consequently there are opened numerouspossible applications in which the composite material according to theinvention can be used.

The process according to the invention also has the advantage thathydrophobic composite materials can be made without the need to performadditional cost-intensive, time-consuming and/or energy-intensiveprocess steps.

The composite material according to the invention will be describedhereinafter by reference to an example, without limiting the compositematerial according to the invention to this type of embodiment.

The permeable composite material according to the invention, whichmaterial exhibits hydrophobic properties, is provided with at least oneporous and permeable support as basis. On at least one side of thesupport and in the interior of the support the support is provided withat least one inorganic component, which substantially contains at leastone compound of at least one metal, at least one semi-metal or at leastone mixed metal with at least one element of Group 3 to Group 7. As usedin the present invention, the term interior of a support refers tocavities or pores in a support.

Preferably the interior and exterior or the interior and the exteriorsurfaces of the composite material according to the invention are coatedwith hydrophobic layers. These layers can contain at least alkyl,fluoroalkyl and/or aryl groups. The interior and/or exterior surfaces ofthe composite material can also be coated, however, with wax and/orpolymer layers. The polymer layers can contain hydrophobic materialschosen from polyethylene, polyvinyl chloride, polystyrene,polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidenechloride, polyisoprene, polybutadiene, heat-treated polyimide,heat-treated polyether imide, polysulfone, polyether sulfone,polyacrylate, polyimidazole or a mixture of these polymers. Preferablythe hydrophobic material present in the hydrophobic layers has a meltingand/or softening point below 500° C.

The composite material according to the invention, which materialexhibits hydrophobic properties, preferably contains a proportion ofhydrophobic material of from 0.0001 wt % to 40.0 wt %, especiallypreferably from 0.01 to 20 wt %.

Depending how the composite material according to the invention withhydrophobic characteristics is made, it is conceivable that thehydrophobic material will differ chemically and physically or chemicallyor physically from the material used to make the composite material.

According to the invention, the porous and permeable support can haveinterstices with a size of 1 nm to 500 μm. The interstices can be pores,meshes, holes, crystal lattice interstices or cavities The support cancontain at least one material chosen from carbon, metals, alloys, glass,ceramics, minerals, plastics, amorphous substances, natural products,composite substances or from at least one combination of thesematerials. It is permissible for supports which can contain the saidmaterials to have been modified by a chemical, thermal or mechanicaltreatment method or a combination of treatment methods. Preferably thecomposite material is provided with a support which contains at leastone metal, one natural fiber or one plastic, which was modified by atleast one mechanical forming technique or treatment method, such asdrawing, upsetting, fulling, rolling, stretching or forging. Quiteparticularly preferably the composite material is provided with at leastone support which contains at least woven, bonded, felted or ceramicallybound fibers or at least sintered or bonded shapes, globules orparticles. In a further preferred embodiment there can be used aperforated support. Permeable supports can also be such which become orhave been made permeable by laser treatment or ion beam treatment.

It can be advantageous if the support contains fibers of at least onematerial chosen from carbon, metals, alloys, ceramics, glass, minerals,plastics, amorphous substances, composite substances and naturalproducts or fibers of at least one combination of these materials, suchas asbestos, glass fibers, carbon fibers, metal wires, steel wires,steel-wool fibers, polyamide fibers, coconut fibers, coated fibers.Preferably there are used supports containing woven fibers of metal oralloys. Wires can also be used as metal fibers. Quite especiallypreferably the composite material is provided with a support whichcontains at least one fabric of steel or stainless steel, such as afabric made by weaving from steel wires, steel fibers, stainless-steelwires or stainless-steel fibers, which fabric preferably has mesh widthsof 5 to 500 μm, especially preferably mesh widths of 50 to 500 μm, andquite especially preferably mesh widths of 70 to 120 μm.

The support of the composite material, however, can also comprise atleast one expanded metal with a pore size of 5 to 500 μm. According tothe invention, however, the support can also comprise at least onegranular, sintered metal, a sintered glass or a metal fleece with a porewidth of 0.1 μm to 500 μm, preferably of 3 to 60 μm.

The composite material according to the invention is preferably providedwith at least one support which contains at least aluminum, silicon,cobalt, manganese, zinc, vanadium, molybdenum, indium, lead, bismuth,silver, gold, nickel, copper, iron, titanium, platinum, stainless steel,steel, brass, an alloy of these materials or a material coated with Au,Ag, Pb, Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.

The inorganic component present in the composite material according tothe invention can contain at least one compound of at least one metal,semi-metal or mixed metal with at least one element of Group 3 to Group7 of the Periodic Table or at least one mixture of these compounds. Thecompounds of the metals, semi-metals or mixed metals can thereforecontain at least elements of the subgroups and of Group 3 to Group 5 orat least elements of the subgroups or of Group 3 to Group 5, thesecompounds having a particle size of 0.001 to 25 μm. Preferably theinorganic component contains at least one compound of an element ofSubgroup 3 to Subgroup 8 or at least one element of Group 3 to Group 5with at least one of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C,Ga, Al or B or at least one compound of an element of Subgroup 3 toSubgroup 8 or at least one element of Group 3 to Group 5 with at leastone of the elements Te, Se, S, O, Sb, As, P, N, Ge, Si, C, Ga, Al or Bor a mixture of these compounds. Especially preferably the inorganiccomponent containing at least one compound of at least one of theelements Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, Ga, In, Tl,Si, Ge, Sn, Pb, Sb or Bi with at least one of the elements Te, Se, S, O,Sb, As, P, N, C, Si, Ge or Ga, such as TiO₂, Al₂O₃, SiO₂, ZrO₂, Y₂O₃,BC, SiC, Fe₃O₄, SiN, SiP, nitrides, sulfates, phosphides, silicides,spinels or yttrium aluminum garnet, or of one of these of the elementsthemselves. The inorganic component can also contain aluminosilicates,aluminum phosphates, zeolites or partly exchanged zeolites, such asZSM-5, Na ZSM-5 or Fe ZSM-5 or amorphous microporous mixed oxides, whichcan contain up to 20% non-hydrolyzable organic compounds, such asvanadium oxide silica glass or alumina silica methylsilicon sesquioxideglasses.

Preferably at least one inorganic component is present in aparticle-size fraction with a particle size of 1 to 250 nm or with aparticle size of 260 to 10,000 nm.

It can be advantageous if the composite material according to theinvention contains at least two particle-size fractions of at least oneinorganic component. Likewise it can be advantageous if the compositematerial according to the invention contains at least two particle-sizefractions of at least two inorganic components. The particle-size ratiocan range from 1:1 to 1:10,000, preferably from 1:1 to 1:100. Thequantitative ratio of the particle-size fractions in the compositematerial can preferably range from 0.01:1 to 1:0.01.

The permeability of the composite material according to the invention islimited by the particle size of the at least one inorganic componentused to particles with a particular maximum size.

The inorganic-component-containing suspension, by means of which thecomposite material according to the invention is obtainable, can containat least one liquid chosen from water, alcohol and acid or a combinationof these liquids.

In a particularly preferred embodiment of the composite materialaccording to the invention which exhibits hydrophobic properties, thesaid composite material can be made bendable without destroying theinorganic component solidified in the interior of the support and/or onthe support. Preferably the composite material according to theinvention is bendable to a minimum radius of as small as 1 mm.

The pore sizes of the permeable composite material exhibitinghydrophobic properties is preferably from 1 nm to 0.5 μm.

The process according to the invention for making a permeable compositematerial according to at least one of claims 1 to 9 will be describedhereinafter with reference to an example, without being limited thereto.

According to the invention, the known hydrophobing methods, which areused among other purposes for textiles (D. Knittel; E. Schollmeyer;Melliand Textilber. (1998) 79(5) 362-363), can also be used, with minormodification of the formulations, for porous permeable compositematerials made, for example, by the process described in PCT/EP98/05939.For this purpose a permeable composite material is treated with asolution containing at least one hydrophobic substance. It can beadvantageous if the solution contains as the solvent water, preferablyadjusted to a pH of 1 to 3 by means of an acid, preferably acetic acidor hydrochloric acid, and/or an alcohol, preferably ethanol. Theproportion of acid-treated water or of alcohol in the solvent can rangefrom 0 to 100 vol %. Preferably the proportion of water in the solventranges from 0 to 60 vol % and the proportion of alcohol from 40 to 100vol %. The solution is prepared by adding 0.1 to 30 wt %, preferably 1to 10 wt % of a hydrophobic substance to the solvent. Silanes, forexample, can be used as hydrophobic substances. Surprisingly, not onlyis good hydrophobing achieved with highly hydrophobic agents such astriethoxy-(3,3,4,4,5,5,6,6,7,7,8,8-tridecafluorooctyl)silane, but thedesired effect is also achieved completely adequately by a treatmentwith methyltriethoxysilane or i-butyltriethoxysilane. The solutions arestirred at room temperature to distribute the hydrophobic substanceshomogeneously in the solution.

The permeable composite material can be treated by dipping, spattering,spraying or similar suitable method. After the composite material hasbeen treated with the solution, it is dried at temperatures of 50 to200° C., preferably at temperatures of 80 to 150° C. After drying thereis obtained a permeable composite material which exhibits hydrophobicproperties.

Preferably a composite material as described in PCT/EP98/05939 is used.In this process for making a permeable composite material, at least onesuspension containing at least one inorganic component comprising atleast one compound of at least one metal, one semi-metal or one mixedmetal with at least one of the elements of Group 3 to Group 7 is appliedin and on at least one porous and permeable support, and the suspensionis solidified on or in or on and in the support material by at least oneheat treatment.

In this process it can be advantageous to apply the suspension on and inor on or in at least one support by forcing on, pressing on, pressingin, rolling on, doctoring on, spreading on, dipping, spattering orpouring on.

The porous and permeable support on which or in which or on and in whichat least one suspension is applied can contain at least one materialchosen from carbon, metals, alloys, ceramics, minerals, plastics,amorphous substances, natural products, composite substances, compositematerials or from at least one combination of these materials. As thepermeable support there can also be used such made permeable bytreatment with laser beams or ion beams. Preferably fabrics of fibers orwires of the materials cited hereinabove are used as supports, examplesbeing metal fabrics or plastic fabrics.

The suspension used, which can contain at least one inorganic componentand at least one metal oxide sol, at least one semi-metal oxide sol orat least one mixed metal oxide sol or a mixture of these sols, can beprepared by suspending at least one inorganic component in at least oneof these sols.

The sols are obtained by hydrolyzing at least one compound, preferablyat least one metal compound, at least one semi-metal compound or atleast one mixed-metal compound with at least one liquid, one solid orone gas, in which process it can be advantageous if water, alcohol or anacid, for example, is used as the liquid, ice as the solid or steam asthe gas, or if at least one combination of these liquids, solids orgases is used. It can also be advantageous to add the compound to behydrolyzed to alcohol or an acid or a combination of these liquidsbefore hydrolysis. As the compound to be hydrolyzed there is preferablyhydrolyzed at least one metal nitrate, one metal chloride, one metalcarbonate, one metal alcoholate compound or at least one semi-metalalcoholate compound, especially preferably at least one metal alcoholatecompound, one metal nitrate, one metal chloride, one metal carbonate orat least one semi-metal alcoholate compound chosen from the compounds ofthe elements Ti, Zr, Al, Si, Sn, Ce and Y or of the lanthanoids andactinoids, such as titanium alcoholates, for example titaniumisopropylate, silicon alcoholates, zirconium alcoholates, or a metalnitrate, such as zirconium nitrate.

In this process it can be advantageous to perform the hydrolysis of thecompounds to be hydrolyzed with at least half the molar ratio of water,steam or ice relative to the hydrolyzable group of the hydrolyzablecompound.

The hydrolyzed compound can be peptized with at least one organic orinorganic acid, preferably with a 10 to 60% organic or inorganic acid,especially preferably with a mineral acid chosen from sulfuric acid,hydrochloric acid, perchloric acid, phosphoric acid and nitric acid or amixture of these acids.

There can be used not only sols prepared as described hereinabove, butalso commercial sols such as titanium nitrate sol, zirconium nitrate solor silica sol.

It can be advantageous if at least one inorganic component with aparticle size of 1 to 10,000 nm is suspended in at least one sol.Preferably there is suspended an inorganic component containing at leastone compound chosen from metal compounds, semi-metal compounds, mixedmetal compounds and metal mixed compounds with at least one of theelements of Group 3 to Group 7, or at least one mixture of thesecompounds. Especially preferably there is suspended at least oneinorganic component containing at least one compound comprising theoxides of the subgroup elements or the elements of Group 3 to Group 5,preferably oxides chosen from the oxides of the elements Sc, Y, Ti, Zr,Nb, Ce, V, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb and Bi,examples being Y₂O₃, ZrO₂, Fe₂O₃, Fe₃O₄, SiO₂, Al₂O₃. The inorganiccomponent can also contain aluminosilicates, aluminum phosphates,zeolites or partly exchanged zeolites, such as ZSM-5, Na ZSM-5 or FeZSM-5 or amorphous microporous mixed oxides, which can contain up to 20%nonhydrolyzable organic compounds, such as vanadium oxide silica glassor alumina silica methylsilicon sesquioxide glasses.

Preferably the proportion by weight of the suspended component amountsto 0.1 to 500 times the hydrolyzed compound used.

Freedom from cracks in the permeable composite material can be optimizedby appropriate choice of the particle size of the suspended compounds asa function of the size of the pores, holes or interstices of the porouspermeable support, and also by the layer thickness of the compositematerial according to the invention as well as by the proportional ratioof sol, solvent and metal oxide.

In order to increase freedom from cracks in the use of a mesh fabricwith a mesh width of 100 μm, for example, there can preferably be usedsuspensions which contain a suspended compound with a particle size ofat least 0.7 μm In general, the ratio of particle size to mesh or poresize should range from 1:1000 to 50:1000. The composite materialaccording to the invention can preferably have a thickness of 5 to 1000μm, especially preferably 50 to 150 μm. The suspension of sol andcompounds to be suspended preferably has a ratio of sol to compounds tobe suspended ranging from 0.1:100 to 100:0.1, preferably from 0.1:10 to10:0.1 parts by weight.

The suspension present on or in or on and in the support is solidifiedin this process by heating this composite to 50 to 1000° C. In a specialalternative embodiment of this process, this composite is exposed to atemperature of 50 to 100° C. for 10 minutes to 5 hours. In a furtherspecial embodiment of the process according to the invention, thiscomposite is exposed to a temperature of 100 to 800° C. for 1 second to10 minutes.

In this process the heat treatment of the composite can be accomplishedby means of heated air, hot air, infrared radiation, microwave radiationor electrically generated heat. In a further special embodiment of thisprocess it can be advantageous if the heat treatment of the composite isperformed using the support material for electrical resistance heating.For this purpose the support can be connected to a current source via atleast two contacts. With the current turned on the support becomesheated in proportion to amperage of the current source and amplitude ofthe output voltage, and the suspension present in and on its surface canbe solidified by this heating.

In a special embodiment of the process according to the invention, thepermeable composite material which exhibits hydrophobic properties canbe made by using, in the process for making a permeable compositematerial described hereinabove and in PCT/EP98/05939 a sol and/or asuspension to which finely divided waxes and/or polymers are added.During solidification of the sol or of the suspension, the waxes and/orpolymers are melted at temperatures below 500° C. and surround theparticles as a thin film, so that the entire interior and exteriorsurface of the composite material is covered by a thin wax and/orpolymer layer. For this purpose there can be used almost all knownpolymers or waxes which melt and/or can flow below 500° C., such aspolyethylene, polypropylene, polyvinyl chloride, polystyrene,polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidenechloride, polyisoprene, polybutadiene, polyimide, polyether imide,polysulfone, polyether sulfone, polyacrylate, polymethacrylate,polyimidazole or a mixture of these polymers. The waxes and/or polymersdo not have to exist as hydrophobic materials, but it is completelyadequate when they acquire the hydrophobic properties during the heatingphase at a temperature of up to 500° C. by a chemical and/or physicalmodification of their structure.

In a further embodiment of the process according to the invention,permeable composite materials can be made by adding alkylsilanes,arylsilanes or fluoroalkylsilanes to a sol prepared as describedhereinabove or to a suspension prepared as described hereinabove, withwhich sol or suspension a support is treated in the manner describedhereinabove or in PCT/EP98/05939. During the solidification processthere takes place partial but adequate orientation of the alkyl, aryl orfluoroalkyl chains, thus imparting a hydrophobic finish to the surfaces.The heat treatment at up to 500° C. does not lead to any substantialdegradation of the alkyl components. Such a hydrophobed permeablecomposite material can be used at temperatures up to 250° C.

By means of the types of processes described here for making permeablecomposite materials which exhibit hydrophobic properties, there are madeaccessible, in completely hydrophobed form, materials with pore sizes inthe range of 1 nm to 0.5 μm.

The permeable composite materials according to at least one of claims 1to 9, which materials exhibit hydrophobic properties, can be used inseveral areas of separation of substances. In this regard theapplications described hereinafter merit special mention, butapplication of the composite materials is not limited thereto.

The composite material according to the invention can be used as themembrane for membrane distillation. Membranes used for membranedistillation are characterized in that the liquid substance mixture tobe separated by distillation must not wet the membranes. At the sametime the membranes must be highly thermally stable and must not undergochanges at higher temperatures. In addition, higher distillationtemperatures are often accompanied by process-related advantages. Thepermeable composite materials according to the invention, whichmaterials exhibit hydrophobic properties, are to be preferred to theknown membranes in membrane distillations, since they can be used over abroader temperature range without suffering changes in their properties,and at the same time they can be made in a wide range of pore sizes andcan be made with thicknesses of less than 100 μm.

The composite material according to the invention can also be used forpervaporation. Just as in membrane distillation, process-relatedadvantages are also achieved during use in pervaporation of thedescribed hydrophobic, permeable composite materials according to theinvention. By virtue of their greater thermal stability, the describedcomposite materials are superior to the conventional materials inorganophilic pervaporation. In a special embodiment of the hydrophobicpermeable composite materials, organic molecules migrate through morerapidly than water, and so organics can be selectively separated fromaqueous solutions in this way.

The composite material according to the invention can also be used as amembrane for vapor permeation. The basis of this process, whichresembles pervaporation, is the same mechanism of permeation through aselective membrane as for pervaporation, and so it is clear thatseparation of organics with a special embodiment of the compositematerial is possible here also. Thermal stability of the material isparticularly important in this case, since vapor permeation sometimestakes place at very high temperatures. The composite materials accordingto the invention can also be used as membranes to enhance theimpregnation of liquids with gases. The problem of impregnation ofaqueous liquids with gases is that the gas bubbles are often very largeand therefore have a relatively small surface. This can be improved bythe use of membranes for impregnation of these fluids with air or othergases. For this purpose the gas is forced through the pores of amembrane into the fluid. The very small bubbles (depending on the chosenpore radius of the membrane) have a very much larger specific surfacethan bubbles introduced into a fluid by other techniques (M. J. Semmens;C. J. Gantzer, M. J. Bonnette, U.S. Pat. No. 5,674,433). However,pressures greater than the “bubble point” of the corresponding membranemust be applied (up to 30 to 40 bar depending on pore size). In the useof hydrophobic permeable composite materials for such aeration ofhydrophilic fluids, the pressures merely have to be higher than thehydrostatic pressure of the fluid, since the fluid cannot penetrate intothe pores and thus the associated effects of pore filling and theresulting high “bubble point” do not occur.

The composite materials according to the invention can also be used forconcentrating heat-sensitive products. Concentration or dewatering ofhighly heat-sensitive products can be accomplished by a special moduleconfiguration using hydrophobic permeable composite materials. In theprocess the fluid to be concentrated (such as a fruit juice) is passedalong one side of the hydrophobic partition while an externally preparedconcentrated salt solution is passed along the other side. Since thepartition is hydrophobic, no contact takes place between the twoliquids. Nevertheless, water-vapor exchange can occur via the gas spaceof the pores and so, by virtue of the different osmotic pressure, thesalt solution can absorb water and the product to be dewatered can giveup water.

A composite material according to the invention can also be used formembrane filtration. Filtration of the most diverse products by means ofmembranes frequently encounters the problem that the filtrate output isinfluenced by formation of surface layers. While this so-called foulingcan be suppressed by the use of highly hydrophilic membranes, it canalso be suppressed by the use of hydrophobic filter materials. Infiltration tests using hydrophobic permeable composite materials, theflow always increases in particular when organics are being filtered andthe fouling layers consist of highly hydrophilic deposits.

The performance gains by the use of hydrophobic permeable compositematerials can range from 10% to 80% in such an arrangement.

The composite materials according to the invention can also be used asmembrane reactors. For certain designs of membrane reactors, it can beadvantageous to use hydrophobic membranes. These are advantageous inmembrane reactors when hydrophobic and hydrophilic constituents of thereaction mixture must be separated from each other or selectivelymetered through a membrane. In these cases the hydrophobic permeablecomposite materials according to the invention are highly suitablesince, as already pointed out, they exhibit constant properties over arelatively broad temperature range. The composite materials according tothe invention can be used, for example, as membranes in membranereactors in which oxidation of aromatics is taking place, for examplethe direct oxidation of benzene to phenol.

FIG. 1 schematically shows a practical example of the hydrophobicpermeable composite material according to the invention.

FIG. 1 schematically shows a concentration cell. This is divided by thehydrophobic permeable composite material M into two compartments. LiquidA1 from which water is to be removed flows into one compartment. Thisliquid can be, for example, a fruit juice. A liquid B1 for absorption ofwater flows into the other compartment. This liquid can be, for example,a concentrated salt solution. Because of the hydrophobic permeablecomposite material, water from the fruit juice can pass over in the formof vapor into the concentrated salt solution. Since both solutions (A1and B1) contain predominantly water, however, direct intermixing of thesolutions is prevented by the hydrophobic properties of the compositematerial. Solution A2 depleted of water is transferred out of the onecompartment, and the salt solution B2 that has absorbed water istransferred out of the other compartment.

The composite material according to the invention, the process accordingto the invention for making the said composite material, and the use ofthe same will be described in more detail in the following examples,without being limited thereto.

EXAMPLE 1.1

Making a Composite Material By the Process Described in PCT/EP98/05939

120 g of titanium tetraisopropylate was intensively stirred with 140 gof deionized ice until ultrafine dispersion of the resultingprecipitate. After addition of 100 g of 25% hydrochloric acid, stirringwas continued until the phase became clear and 280 g of type CT3000SGα-alumina from Alcoa of Ludwigshafen was added, after which stirring wascontinued for several days until disintegration of the aggregates. Athin layer of this suspension was then applied on a metal gauze andsolidified at 550° C. within the shortest possible time.

EXAMPLE 1.2.a

Hydrophobing of Already Existing Composite Materials

A composite material made according to Example 1.1 was dipped in asolution comprising the following components: 1% Dynasilan F 8261, 2%demineralized water acidified to pH 2.5 with acetic acid, and 97%ethanol. Before use, the solution had to be stirred for 5 hours at roomtemperature. After supernatant solution had been allowed to drip off,the composite material was dried at 80° C. to 150° C. and then used.

EXAMPLE 1.2.b

Hydrophobing of Already Existing Composite Materials

A composite material made according to Example 1.1 was dipped in asolution comprising the following components: 5% methyltriethoxysilane,0.5% hydrochloric acid (35%), 40% ethanol and 54.5% demineralized water.Before use, the solution had to be stirred for about 10 minutes at roomtemperature. After supernatant solution had been allowed to drip off,the composite material was dried at 80° C. to 150° C. and then used.

EXAMPLE 1.3.a.1

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

50 g of titanium tetraisopropylate and 40 g Dynasilan F 8261 wereintensively stirred with 130 g of deionized ice until ultrafinedispersion of the resulting precipitate. After addition of 100 g of 25%hydrochloric acid, stirring was continued until the phase became clearand 280 g of type CT3000SG α-alumina from Alcoa of Ludwigshafen wasadded, after which stirring was continued for 3 days untildisintegration of the aggregates. This suspension was then applied on astainless-steel fabric and solidified at about 500° C. within theshortest possible time.

EXAMPLE 1.3.a.2

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

50 g of titanium tetraisopropylate and 30 g i-butyltriethoxysilane wereintensively stirred with 130 g of deionized ice until ultrafinedispersion of the resulting precipitate. After addition of 100 g of 25%hydrochloric acid, stirring was continued until the phase became clearand 280 g of type CT3000SG α-alumina from Alcoa of Ludwigshafen wasadded, after which stirring was continued for several days untildisintegration of the aggregates. This suspension was then applied on awire gauze and solidified at about 500° C. within the shortest possibletime.

EXAMPLE 1.3.a.3

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

50 g of titanium tetraisopropylate and 30 g methyltriethoxysilane wereintensively stirred with 130 g of deionized ice until ultrafinedispersion of the resulting precipitate. After addition of 100 g of 25%hydrochloric acid, stirring was continued until the phase became clearand 280 g of type CT3000SG α-alumina from Alcoa of Ludwigshafen wasadded, after which stirring was continued for several days untildisintegration of the aggregates. This suspension was then applied on awire gauze and solidified at 500° C. within the shortest possible time.

EXAMPLE 1.3.b.1

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

60 g of tetraethyl orthosilicate and 40 g of Dynasilan F 8261 wereintensively stirred with 120 g of deionized ice until ultrafinedispersion of the resulting precipitate. After addition of 40 g of 65%nitric acid, stirring was continued until the phase became clear. 280 gof type CT530SG α-alumina from Alcoa of Ludwigshafen was added, afterwhich the sol was stirred for 3 days until disintegration of allaggregates. This suspension was then applied on an aluminum gauze andsolidified at 500° C. within the shortest possible time.

EXAMPLE 1.3.b.2

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

The experiment from Example 1.1.b.1 was repeated, but 40 g ofmethyltriethoxysilane was used instead of the Dynasilan F 8261.

EXAMPLE 1.3.b.1

Hydrophobing By Addition of Silanes to the Sol For Making the CompositeMaterial

The experiment from Example 1.1 .b.1 was repeated, but 40 g ofi-butyltriethoxysilane was used instead of the Dynasilan F 8261.

EXAMPLE 1.4.a.1

Hydrophobing By Addition of Waxes and/or Polymers

80 g of titanium tetraisopropylate was hydrolyzed with 20 g of water,and the resulting precipitate was peptized with 120 g of nitric acid(25%). This solution was stirred until it became clear and, afteraddition of 40 g of titanium dioxide from Degussa (P25) and 5 g ofpolytetrafluoroethylene powder, stirring was continued untildisintegration of the agglomerates. This suspension was then applied ona porous support corresponding to Example 1.1 and solidified at 500° C.within the shortest possible time.

EXAMPLE 1.4.a.2

Hydrophobing By Addition of Waxes and/or Polymers

The experiment was repeated with the same parameters as in Example1.4.a.1. 5 g of polyethylene was used instead of 5 g ofpolytetrafluoroethylene.

EXAMPLE 1.4.a.3

Hydrophobing By Addition of Waxes and/or Polymers

The experiment was repeated with the same parameters as in Example1.4.a.1. 5 g of polypropylene was used instead of 5 g ofpolytetrafluoroethylene.

EXAMPLE 1.4.b

Hydrophobing By Addition of Waxes and/or Polymers

80 g of titanium tetraisopropylate was hydrolyzed with 20 g of water,and the resulting precipitate was peptized with 120 g of nitric acid(25%). This solution was stirred until it became clear and, afteraddition of 40 g of titanium dioxide from Degussa (P25) and 15 g ofpolyimide powder, stirring was continued until disintegration of theagglomerates. This suspension was then applied on a porous supportcorresponding to Example 1.1 and solidified at 500° C. within theshortest possible time. In this case good hydrophobing is achieved onlyafter complete transformation (carbonization and imidization) of thepolyimide.

EXAMPLE 1.5

Measurements of the Contact Angle

The following table presents the results of measurements of the contactangle by the resting-drop method for water against air, performed on thecomposite materials made in Examples 1.1 to 1.4.b.

Example Hydrophobing component Contact angle [°] 1.1 —  0 1.2.a.Dynasilan F 8261 145 1.2.b Methyltriethoxysilane 136 1.3.a.1 Dynasilan F8261 139 1.3.a.2 Methyltriethoxysilane 134 1.3.a.3i-Butyltriethoxysilane 110 1.3.b.1 Dynasilan F 8261 141 1.3.b.2Methyltriethoxysilane 134 1.3.b.3 i-Butyltriethoxysilane 109 1.4.a.1Polytetrafluoroethylene 148 1.4.a.2 Polyethylene 132 1.4.a.3Polypropylene 136 1.4.b Polyimide 108

What is claimed is:
 1. A permeable composite material, comprising: atleast one porous and permeable support which is flexible and which isprovided on at least one side thereof and in the interior thereof withan inorganic component, which comprises substantially a compound of ametal, a semi-metal and/or a mixed metal of at least one element ofGroup III to Group VII of the Periodic Table, the permeable compositematerial being hydrophobic and having a thickness ranging from 5 to1,000 μm.
 2. The permeable composite material according to claim 1,wherein the interior and exterior or the interior or exterior surfacesof the composite material are coated with hydrophobic layers.
 3. Thepermeable composite material according to claim 2, wherein the interiorand/or exterior surfaces of the composite material are coated with atleast one layer containing alkyl, fluoroalkyl and/or aryl groups.
 4. Thepermeable composite material according to claim 2, wherein the compositematerial is coated on the interior and/or exterior surfaces with a waxand/or a polymer layer.
 5. The permeable composite material according toclaim 2, wherein the hydrophobic material present in the hydrophobiclayers has a molting and/or softening point below 500° C.
 6. Thecomposite material according to claim 2, wherein the hydrophobic layerscontain at least one hydrophobic material selected from the groupconsisting of polyethylene, polypropylene, polyvinyl chloride,polystyrene, polytetrafluoroethylene, polyvinylidene fluoride,polyvinylidene chloride, polyisoprene, polybutadiene, heat-treatedpolyimide, heat-treated polyether imide, polysulfone, polyether sulfone,polyacrylate, polymethacrylate, polyimidazole and a mixture of thesepolymers.
 7. The permeable composite material according to claim 1,wherein the hydrophobic permeable composite material contains aproportionate amount of hydrophobic material ranging from 0.0001 to 40wt. %.
 8. The permeable composite material according to claim 7, whereinthe hydrophobic permeable composite material contains a proportionateamount of hydrophobic material ranging from 0.01 to 20 wt. %.
 9. Thepermeable composite material according to claim 1, wherein thehydrophobic material differs chemically and physically or chemically orphysically from the material employed to make the composite material.10. The permeable composite material according to claim 1, wherein thehydrophobic permeable composite material has a thickness ranging from 50to 150 μm.
 11. The permeable composite material according to claim 1,wherein the hydrophobic permeable composite material is bendable to aminimum radius as small as 1 mm.
 12. The permeable composite materialaccording to claim 1, wherein the inorganic component has a particlesize fraction of a particle size of 1 to 250 nm.
 13. The permeablecomposite material according to claim 12, wherein the inorganiccomponent has a particle size fraction of a particle size of 260 to10,000 nm.
 14. The permeable composite material according to claim 12,wherein the composite material comprises at least two particle sizefractions of one or two inorganic component(s), wherein the particlesize ratio of the fractions ranges from 1:1 to 1:10,000.
 15. Thepermeable composite material according to claim 14, wherein the ratio ofthe fractions ranges from 1:1 to 1:100.
 16. The permeable compositematerial according to claim 1, wherein the support comprises fibers ofat least one material selected from the group consisting of carbon,metals, alloys, ceramics, glass, minerals, plastics, amorphoussubstances, composite substances and natural fibers.
 17. The permeablecomposite material according to claim 16, wherein the support comprisesfibers which are asbestos, glass fibers, carbon fibers, metal wires,steel wires, steel-wool fibers, polyamide fibers, coconut fibers orcoated fibers.
 18. The permeable composite material according to claim1, wherein the support is in woven, bonded, felted or ceramically boundfibers or in a sintered or bonded shape, as globules or particles.
 19. Aprocess for making a permeable composite material according to claim 1,in which at least one suspension which contains at least one of saidinorganic component and a sol, is applied on at least one porous andpermeable support, and this suspension is solidified on or in or on andin the support material by at least one heat treatment, wherein at leastone of the inorganic components used exhibits hydrophobic propertiesand/or at least one hydrophobic material and/or one hydrophobing agentis added to the sol and/or to the suspension.
 20. A process according toclaim 10, wherein the sol and/or the suspension contains hydrophobicmaterials, hydrophobic particles and/or hydrophobing substances.
 21. Aprocess according to claim 11, wherein the hydrophobic materials orparticles have a melting or softening point below 500° C.
 22. A processaccording to claim 11, wherein the hydrophobic material is a wax and/ora polymer and/or an alkylsilane, fluoroalkylsilane or arylsilane.
 23. Aprocess according to claim 11, wherein the hydrophobic material is,selected from polyethylene, polypropylene, polyvinyl chloride,polystyrene, polytetrafluoroethylene, polyvinylidene fluoride,polyvinylidene chloride, polyisoprene, polybutadiene, polyimide,polyether imide, polysulfone, polyether sulfone, polyacrylate,polymethacrylate, polyimidazole or a mixture of these polymers.
 24. Aprocess according to claim 11, wherein the sol contains from 0.001 wt %to 50 wt % of hydrophobic or hydrophobing material.
 25. A processaccording to claim 15, wherein the sol contains from 0.01 wt % to 25 wt% of hydrophobic or hydrophobing material.
 26. A process according toclaim 11, wherein the hydrophobic or hydrophobing material or thepolymer or the wax is modified chemically and physically or chemicallyor physically by a treatment.
 27. The composite material according toclaim 1 which is capable of being used as a membrane for membranedistillations.
 28. The composite material according to claim 1, which iscapable of being used in pervaporation.
 29. The composite materialaccording to claim 1, which is capable of being used in vaporpermeation.
 30. The composite material according to claim 1, which iscapable of being used for concentration of heat-sensitive substances.31. The composite material according to claim 1, which is capable ofbeing used as a membrane in membrane reactors.
 32. The compositematerial according to claim 1, which is capable of being used as amembrane in membrane filtration.
 33. The composite material according toclaim 1, which is capable of being used for impregnation of liquids withgases.
 34. A permeable composite material, comprising: at least oneporous and permeable support which is flexible and which is provided onat least one side thereof and in the interior thereof with aproportionate amount of inorganic component of 0.0001 to 40.0 wt. %,which comprises substantially a compound of a metal, a semi-metal and/ora mixed metal of at least one element of Group III to Group VII of thePeriodic Table, the permeable composite material being hydrophobic andhaving a thickness ranging from 5 to 1,000 μm.
 35. The permeablecomposite material according to claim 25, wherein the permeablecomposite material further comprises an alkylsilane, arylsilane orfluoroalkylsilane support in its structure.